I. Background and Significance A. Historical Background and Scientific Basis Background The most common cause of withdrawal or restriction of drugs that are already on the market is prolongation of the QT interval, and the consequent, potentially fatal, arrhythmia, torsade de pointes1. First described in the 1960s with quinidine therapy2, torsade de pointes occurs most commonly with antiarrhythmics3, although sudden cardiac death risk is increased 270% with use of a non-cardiac QT-prolonging medication4.